Hair treatment method involving irradiation through an optical medium

ABSTRACT

Hair treatment method in which at least one portion of at least one hair (H) is exposed to at least one pulse of light through a fluid or solidified transparent medium (M) with a refractive index of 1.3 or higher, this medium being in contact with the hair or hairs and extending between the hair or hairs and a surface (I) at which light enters the medium, preferably of predefined form.

The present invention relates to the cosmetic treatment of human oranimal keratin fibers. The invention more particularly relates to hairtreatments by irradiation.

Many hair treatments use light for treating the hair, for example formore or less substantially bleaching the melanin.

Applications U.S. Pat. No. 4,792,341, U.S. Pat. No. 5,246,019, U.S. Pat.No. 5,303,722, EP 685 220 A1, EP 682 937 B1 and US 2007 10167936 A1 thusdescribe hair bleaching methods using irradiation devices.

U.S. Pat. No. 5,246,019 discloses the application of a bleachingcomposition (alcoholic or hydro-alcoholic solution, emulsion or gel)present on the hair at the time of irradiation, which irradiationpreferably uses continuous light. Rinsing is then performed.

EP 685 220 teaches of subjecting wet hair to a bleaching treatment withpulsed light.

EP 682 937 teaches of cooling the treated area by circulating a fluid,for example a gas comprising water droplets.

The light must be used so as not to degrade the keratin fibers, andcomplying with irradiation conditions that avoid degradation of thefiber proves to be a constraint on the development of these methods.

It has been proposed to use cooling devices to avoid heating the keratinfibers. However, cooling does not prevent the fibers from being degradedunder certain irradiation conditions and makes the treatment system morecomplex and expensive. Furthermore, cooling devices are generally notsuited to firing frequencies of greater than 100 Hz.

There is a need to benefit from a method for treating hair byirradiation, which is rapid while at the same time limiting the risks ofdegradation of the hair, and the invention is directed toward satisfyingthis need.

A subject of the invention is thus, according to one of its aspects, ahair treatment method in which at least a portion of at least one hairis exposed to at least one light pulse through a transparent medium,which is fluid or which has solidified, with a refractive indexadvantageously of greater than or equal to 1.3 (at 20° C.) and ifpossible greater than 1.4, this medium being in contact with the hairand extending between the hair and a surface of the medium, via whichthe light enters the medium.

The presence of the transparent medium makes it possible to use lightpulses with a peak power of greater than or equal to 10⁵ W, for example,reducing or even eliminating the risk of degradation of the hairs athigh power values. The firing frequency may be greater than or equal to100 Hz, or even 1 kHz or 10 kHz.

The transparent medium also makes it possible to increase the quality ofthe result obtained. As a nonlimiting example, during bleaching, thepresence of the transparent medium makes it possible to bleach the twoopposite faces of a layer of hairs. Advantageously, since the quality isimproved, it is possible to reduce the number of firings or the energyper firing. The risk of degrading the hairs is thus reduced. It is alsopossible to treat thicker locks, since the transparent medium allows theeffect of the light radiations to be propagated to the lower layers ofthe hairs of the lock.

The transparent medium also makes it possible to reduce the odors givenoff.

The shape of the surface for the entry of light into the medium isadvantageously of predefined shape.

The shape of this surface may be defined by a transparent wall of anirradiation device in contact with the transparent medium. Thistransparent wall may be part of an optical channel of the irradiationdevice. The transparent wall may define an optical output of thisirradiation device. As a variant, the transparent wall is intermediatebetween an optical channel for the entry of light and the transparentmedium, and protects, for example, the optical channel from the risk ofsoiling or wetting by the transparent medium. The transparent wall maybe mobile relative to the hairs and/or mobile relative to a hair guidesystem.

The light entry surface may be defined by levelling or flattening themedium, prior to exposure to the light pulse. The light entry surfacemay or may not be in contact with the air.

The levelling or flattening of the medium may be linked to the movementof a treatment system member.

The levelling or flattening may take place manually or be performedautomatically by the treatment system used.

The predefined shape may also be obtained with local fusion of thetransparent medium. A meltable wax may be used. Such a wax may beintroduced in powder form so as to surround the hairs. Applying heatmakes the wax melt.

The transparent medium may be liquid at the time of irradiation. It mayalso be liquid when it comes into contact with the hairs and solidifythereafter, so that it is solid at the time of irradiation. The lightentry surface may have its shape defined while the medium is stillliquid. As a variant, the predefined shape of the entry surface may beobtained after the medium has become solid. The term “solid” includes astate in which the medium is gelled.

The removal of the transparent medium after irradiation may take placeby suction, drying, heating, washing and/or evaporation, according tothe nature of the medium.

The entire section of at least one treated hair may be included in thetransparent medium at the time of irradiation. At least two and betterstill three layers of superposed hairs may be included in thetransparent medium and exposed simultaneously to the light pulse(s). Allthe treated hairs may be at the back of the light entry surface. Asmentioned hereinabove, the transparent medium contributes towarddelivering the light to the hairs of the layers below the first layer,which makes it possible to treat several layers of hairs simultaneously.

The transparent medium may be cooled, where appropriate, for example soas to maintain a temperature of between −50 and 50° C.

The transparent medium may be static relative to the hairs during theirradiation, or may circulate. Circulation of the transparent medium isdirected, for example, toward improving the conduction of heat andavoiding the creation of hot spots.

The treated hair(s) may be confined within a guide system defining thetreatment space containing the hairs and the transparent medium. Thetreatment space may be of constant or adjustable dimensions, for exampleso as to adapt it to the size of a lock to be treated.

The hairs may, where appropriate, be packed into the treatment space.

During the treatment, the hairs may be immobile in the treatment space.As a variant, the treatment space is moved along the hairs during theirradiation. The movement of the treatment space is caused, for example,by moving a transparent wall relative to a hair guide system, this wallcoming into contact with the transparent medium and imposing its shapeon the light entry surface in the transparent medium. The transparentwall may be part of an optical channel, for example one or more opticalfibers, or may be interposed between the optical channel and thetransparent medium. Means may be provided, where appropriate, forcontaining the transparent medium in the treatment space despite themovement of the hairs. The treatment space is, for example, delimited bymedium-confining components comprising, for example, elasticallydeformable joints that are applied against the hairs. The treatmentspace may also be continuously fed with transparent medium, so as toensure that a sufficient amount of transparent medium coats the hairsthat are to be irradiated, taking into account the losses associatedwith the non-leaktightness of the treatment space.

The treatment of the hairs may be performed over a basin for recoveringthe transparent medium. Depending on the nature of the transparentmedium, the recovered medium may be evacuated to the wastewater, forexample if it is pure water or water containing an additive that is notto be recycled, or that is to be at least partially recycled, after anoptional filtration.

A composition whose role is twofold, for example making it possible tobenefit from a high refractive index and to exert another action on thehairs, may be used to prepare the transparent medium. For example,glycerol may be used, which will give the hair an emollient effect.

The transparent medium may be dispensed over the hair from at least oneorifice for delivering said transparent medium, this orifice being ableto be moved relative to the hairs between two light pulses. Delivery ofthe fluid intended to form the transparent medium may take place via adelivery orifice that occupies a variable position relative to a hairguide system.

The light treatment may be directed toward bleaching the hairs and/orgiving them remanent reshaping, which is different than a hair-removaltreatment. During the implementation of the process, it is possible forthe light not to reach the scalp or the skin.

A subject of the invention is also, according to another of its aspects,a treatment system comprising:

-   -   an irradiation device comprising a source of pulsed light,    -   a source of a fluid or solidifiable transparent medium, with a        refractive index of greater than or equal to 1.3,    -   a system for guiding the hairs to be treated, configured so as        to receive the hairs to be treated, the treatment system being        configured to bring the transparent medium into contact with the        hairs and preferably arranged to give a predefined shape to a        surface for the entry of light into the medium.

The treatment system may comprise a source of fluid used for forming thetransparent medium, for example a reservoir containing said fluid, or apipe connecting to a source of said fluid or of a component of themedium, for example a pipe for connecting to a water source and one ormore optional reservoirs of one or more additives to be mixed with waterto form the transparent medium.

The treatment system may bring the transparent medium into contact withthe hairs to be treated. The medium may also be placed on the hairsoutside the hair guide system.

The guide system and the light entry surface may define a treatmentsurface that surrounds the treated hair(s) on all sides, in at least onesection taken transversely relative to the treated hair(s).

The treatment system may comprise a basin for recovering the transparentmedium and also optionally a system for recirculating to the treatmentspace.

The treatment system may comprise a system for cooling the transparentmedium, for example an exchanger in which circulates the medium or acold source in contact with the medium.

The guide system may be arranged to calibrate the amount of haircontained in the treatment space. The cross section of this space has,for example, a thickness corresponding to a relatively small number oflayers of hair, for example less than four layers.

The cross section of the treatment space has, for example, a depth ofbetween 1 mm and 10 mm and a width of between 1 mm and 10 mm.

In one embodiment, the treatment system comprises a transparent wallthat is mobile relative to the guide system. This guide system maydefine a hair-receiving canal, for example of rectangular cross section.The transparent wall may move with an optical output.

One or more orifices for delivering the fluid intended to constitute themedium may emerge into said canal, this or these orifices being located,for example, in the guide system. As a variant, the transparent wallmoves with at least one fluid-delivering orifice, for example defined bya fluid spray nozzle. This or these orifices may be located upstream ofthe transparent wall, with regard to its movement, to ensure goodimpregnation of the hairs.

The system may comprise a delivery orifice emerging into a treatmentspace through which the hairs pass, this orifice being in communicationwith a reservoir and being rigidly attached to an optical output of theirradiation device.

The invention may be understood more clearly on reading the detaileddescription that follows, of nonlimiting embodiments thereof, and onexamining the attached drawing, in which:

FIGS. 1 a and 1 b illustrate a first embodiment of the invention,

FIGS. 2 a and 2 b illustrate a second embodiment of the invention,

FIG. 3 represents, schematically and partially, an example of atreatment system, and

FIG. 4 is a schematic and partial cross section, along IV of FIG. 3; and

FIG. 5 represents another example of a treatment system.

TRANSPARENT MEDIUM

The medium used according to the invention is preferably colorless, butit may be colored provided that it does not significantly absorb theworking wavelength(s) of the irradiation light. For example, the mediummay have an absorption less than or equal to a factor of 10 of thedominant wavelength of the irradiation light.

The transparent medium has a refractive index of greater than or equalto 1.3, preferably greater than or equal to 1.4, or even 1.41, 1.42,1.43, 1.44 or 1.45, at 20° C.

The transparent medium may contain at least one organic compound in amass content of greater than or equal to 1%.

The medium comprises, for example, at least one organic solvent chosenfrom alcohols, polyols, ketones and silicones, and mixtures thereof.

The medium contains, for example, ethanol with a refractive index of1.36, glycerol with a refractive index of 1.47 or acetone with arefractive index of 1.36, for example in an amount by mass of greaterthan or equal to 25% relative to the total weight of the medium.

The medium may also be a fluid that solidifies.

Compositions that are capable of setting to a solid when the solventevaporates off may be used, for example, a concentrated latexcomposition of a material that can coalesce by virtue of its Tg (glasstransition temperature) and/or the presence of plasticizers. Moreover,use may be made of materials which, by chemical reaction or byphysicochemical bonding, can set to a solid, for example a reactivesilicone. The advantage of this approach is that it enables the lightirradiation to be performed without the movements inherent in themanipulations causing the hairs to move relative to each other. Anyrisks of certain parts of the hair being overexposed and other partsunderexposed, in particular when it is desired to perform severalpassages, are thus limited.

Preferably, the medium used is polar and has a capacity for wetting thesurface of the hairs, for instance water or alcohol.

A fast-evaporating fluid may also be used, for instance a light alkanesuch as butane or pentane, an ether, for instance dimethyl ether ordiethyl ether, a volatile silicone, acetone or an alkyl acetate.

The temperature of the transparent medium, at the time of irradiation,may be between −80° C. and 80° C.

The medium may be chemically inert with respect to the hairs. The mediummay especially not produce any photochemical activation of the hairs.The medium may be free of oxidizing agent, especially H₂O₂.

If the illumination is in the UV spectrum, it is possible to use amaterial that filters out UV little or not at all.

Irradiation Device

The invention uses irradiation of keratin fibers via pulsed light, i.e.light pulses. These pulses may be generated in various ways,preferentially using a laser, but other sources, for example a flashlamp, may be envisioned provided that they are able to deliver pulsessuited to the treatment to be performed.

The light used for the treatment according to the invention may have arelatively short pulse duration and a relatively high peak power.

The keratin fibers are, for example, exposed locally, at the same place,to several successive pulses. Advantageously, successive pulses make itpossible to reduce the risk of damaging the keratin fibers, since thefibers are then irradiated gradually.

The pulse duration denotes the time for which the light power reachingthe keratin fibers is greater than or equal to half of its peak power.

The pulse duration is, for example, between 10⁻¹⁶ s and 10⁻⁵ s andbetter still between 10⁻¹⁵ s and 10⁻⁷ s. The duration is, for example,greater than 5×10⁻¹² s or less than or equal to 5×10⁻¹² s.

The number of light pulses to which the same portion of keratin fibersis exposed is controlled, for example, as a function of the surfaceenergy of the radiation that reaches the keratin fibers, the color ofthe keratin fibers and the treatment to be performed.

In a nonlimiting manner, in the case where one or more firings areperformed on the same portion of hair, the firing rate is preferentiallygreater than or equal to 10 Hz and better still 100 Hz, or even greaterthan or equal to 200 Hz, 500 Hz or 1 kHz, and preferentially less than100 kHz.

In a nonlimiting manner, the dominant wavelength of the light reachingthe hairs may be between 300 nm and 10 000 nm and preferentially between400 nm and 2000 nm. The dominant wavelength may be part of the visible,ultraviolet or infrared spectrum.

In a nonlimiting manner, various optical, absorbent or dichroic filtersmay be used so as to filter the light irradiating the fiber, forinstance filters that screen out ultraviolet light or colored filtersfor protecting the natural or artificial color of the hairs. It willpreferably be chosen to illuminate the hairs with a light that is notabsorbed by certain sensitive compounds of the hairs. These coloredfilters make it possible, for example, to remove or greatly reducecertain components of light that correspond, for example, to theabsorption band of hair dyes or to other absorption bands.

The characteristics of the emitted light are, for example, manually orautomatically controlled, optical components being intended, forexample, to be changed or moved so as to modify the focusing or thedominant wavelength of the light. The selection of the wavelength of thelight projected onto the fibers to be treated is, for example, performedautomatically or manually. A user can, for example, manually change anoptical component such as a lens or a filter through which the lightradiation passes during use.

A servomechanism may also be provided to perform automatic control ofirradiation parameters, for example by controlling one or more opticalcomponents, this or these optical component(s) being, for example, movedby means of actuators piloted by one or more command signals. Thesecommand signals are transmitted, for example, by the computing unit ofthe treatment system as a function of data received from one or moresensors, for instance an optical sensor or a camera that can detectdifferent hair colors or natures.

Automatic control may also be performed on the basis at least of answersto a questionnaire concerning the hair of the person to be treated.

The power supply of the irradiation device may be autonomous, forexample portable and integrated into a handpiece.

In a nonlimiting manner, use may be made, to produce the light used forthe treatment, of “attosecond” lasers whose pulse duration ranges from10⁻¹⁸ to 10⁻¹⁵ sec, “femtosecond” lasers whose pulse duration rangesfrom 10⁻¹⁵ sec to 10⁻¹² sec or “picosecond” lasers whose pulse durationranges from 10⁻¹² sec to 1 ns.

It is possible to use flash-pumped lasers, which generally have a pulseduration of about a nanosecond, or diode-pumped lasers, whose pulseduration generally ranges from one nanosecond to about a hundrednanoseconds.

The irradiation device comprises, for example, a laser with a cavityformed by two mirrors located on either side of a broad-band amplifiermaterial, for example based on titanium-sapphire or based on ytterbium.The cavity may also be formed by an optical fiber made of an amplifiermaterial. The irradiation device may comprise a mode-blocking device.

The irradiation device may comprise a lens associated with the laser,with a digital aperture of between, for example, 0.1 and 1, such as alens used for the reading of optical storage disks. The irradiationdevice may also comprise a coupler for injecting the pumping light and acoupler for extracting the laser pulses. The pumping light is produced,for example, by a diode, but may also be produced by a flash lamp or byanother laser.

Irrespective of the light generator used, each of the firings has, forexample, a peak power of 1 MW to 1000 GW and better still 1 MW to 100GW.

The irradiation device uses, for example, a laser whose mean electricalpower is between 0.001 W and 50 W and which delivers, for example, peakpowers ranging from 1 MW to 100 GW.

The number of firings to which the treated portion is subjected is, forexample, between 1 and 10 000 firings and preferentially between 5 and1000 firings.

The light reaching the keratin fibers has, for example, a fluence fromabout 1 to a few J/cm², for example less than 5 J/cm². The fluence mayrange, for example, from 0.1 mJ/mm² to 50 mJ/mm², for example as afunction of the yields, the pulse durations or the adjustments made as afunction of the hair type.

A user interface with, for example, a screen and one or more selectionkeys may make it possible to select among various operating modes and/orto modify the pulse durations, the energy supplied per firing and/or thefiring frequency.

Nonlinear optical components may be used to double or triple thefrequency or to spread out the spectrum of the light reaching thetreated fibers.

The irradiation device may comprise a device for collimating the lightbeam and thus use a less powerful laser for an identical irradiationenergy, but which is nevertheless sufficient to perform the desired hairtreatment. The collimating device is, for example, adjustable so as toadjust the light flux reaching the keratin fibers. This adjustment isperformed manually or automatically, for example as a function of thecolor of the keratin fibers to be treated or as a function of a desireddegree of result. The collimating device may comprise several lenses,which are convergent and/or divergent.

The irradiation device may be used close to the hair or transportationof the light to the transparent medium may be performed. Various opticalcomponents may be used for transporting the light, such as collimationoptics, one or more mirrors and/or optical deflectors and/or an opticalchannel such as one or more optical fibers.

An optical deflector may serve to orient the path of the light rays as afunction of addressing data. The optical deflector is piloted, forexample, by the computing unit to deliver the light beam onto theportion of the keratin fibers to be treated.

The irradiation device may also be equipped with means for confining orabsorbing light, for trapping the light and preventing it from diffusingoutside the treatment area.

The optical output may have any form, and may be single or multiple. Theirradiation device comprises, for example, a circular optical output oran output in the form of one or more slits, which may have variousprofiles.

The optical output may be in contact with the transparent medium.

Treatment Process and System

The treatment process according to the invention may be applied to asingle hair, but preferably to a lock of hair comprising, for example,between 100 and 10 000 hairs.

The process may be applied to a portion of this lock or to severalseparate portions of this lock, or even to the whole lock. The lock thatis irradiated may comprise a single layer of irradiated hair, but thetreatment is preferably performed with several superposed layers ofhair, the treated thickness thus being greater than that of one hair.

FIGS. 1 a and 2 a illustrate the treatment of a lock comprising threesuperposed layers of hair, but, needless to say, the invention is notlimited to a particular number of layers or to a particular regulararrangement of hairs within each layer, the stacking of the hairs in atreatment area possibly being irregular without the various stackedlayers being clearly discernible.

In accordance with one aspect of the invention, at least one hair H isin contact with a transparent medium M that has a refractive index ofgreater than 1.3 and that contributes towards delivering the light tothe hair(s) to be treated.

FIG. 1 b illustrates the possibility for the medium M of not includingall the thickness of the lock and of being in contact, for example, withonly the surface layers thereof.

FIG. 2 b illustrates the possibility of all of the lock being in contactwith the transparent medium M.

The light is delivered to the hair by passing through an entry face I ofthe medium M that advantageously has a predefined shape, for exampleflat as illustrated in FIGS. 1 b and 2 b.

The entry surface of the medium through which the incident light passesduring a firing is, for example, between 10 000 μm² and 100 cm².

The fact that the face I of entry into the medium M has a predefinedshape makes it possible to control the penetration of light into themedium and thus to optimize the amount of light reaching the hairs. Itis also possible to prevent a hair from being irradiated with a largeamount of energy while it is not immersed in the medium.

All the hairs of the first surface layer may thus be located behind theentry surface I.

FIGS. 1 a and 2 a represent the outer surface of the medium M with anirregular shape to illustrate the fact that the light entry surface isnot of predefined shape.

Many possibilities exist for giving the entry surface I a predefinedshape.

It is possible, for example, to flatten or level off the medium so as toimpose its shape on the entry face I, the levelling or flatteningpossibly being performed, for example, manually or automatically.

The user may, for example, move a treatment system member to level thesurface of the medium.

The shape of the surface for the entry of light into the medium may alsobe defined with a transparent wall 10, in contact with the medium M, asillustrated in FIGS. 3 and 4.

These figures show, very schematically and partially, a treatment system15 that comprises an optical channel 16 for delivering light up to thetransparent wall 10 in contact with the medium M.

The hairs H are confined in a guide system 20 that at least partiallydefines the treatment space 21 containing the medium M. The thickness eof this treatment space 21 is, for example, between 1 mm and 5 mm, whichcan receive, for example, between 1 and 20 layers of hair, for examplethree layers.

The width L of the treatment space 21 is, for example, between 5 mm and30 mm.

The medium M present in the treatment space 21 may be delivered thereinin various ways.

For example, the medium M is deposited on the hairs before they enterthe treatment space.

As a variant, the treatment space is fed with transparent medium via theguide system, for example via the sides of the canal in which the hairsextend, for example via one or more orifices 26 that are incommunication with a source of the fluid intended to constitute thetransparent medium.

Where appropriate, a recovery system, not shown, for instance a basin,may be arranged so as to recover the medium that flows via thelongitudinal ends of the canal of the guide system, via which the hairsenter and leave. These longitudinal ends may optionally be provided witha sealing system, for example seals between which the hairs pass.

The treatment system may be arranged to exert a pressure or a tension onthe hairs to be treated, so as to ensure good inclusion of the hairs inthe transparent medium M.

In the example of FIG. 3, the lock of hair is immobile relative to theguide system 20. The transparent wall 10 can move longitudinallyrelative to the guide system 20 to treat the lock extending in the guidesystem.

On moving, the transparent wall 10 presses on the transparent medium M,which ensures its planarity on contact with the transparent wall 10, andthe absence of air also makes it possible to spread out the hairspresent in the guide system.

The movement of the transparent wall 10, which defines the opticaloutput of the irradiation device, relative to the guide system may beeffected manually or, as a variant, automatically, the treatment systemcomprising, for example, an actuator for moving the optical output in amanner slaved to the emission of the light pulses.

Optionally, the dispensing of the fluid intended to constitute thetransparent medium can be slaved to the forward motion of the opticaloutput, so as to make the dispensing of the fluid coincide with thepositioning of the optical output.

It is also possible, in another variant, to arrange for the fluid not tobe dispensed via the orifices of the guide system, but via a part of thetreatment system that comprises the optical output. Preferably, thefluid is dispensed via at least one orifice that is located upstream ofthe optical output with regard to its direction of motion, in order forthe fluid to have the time to impregnate the hairs before the arrival ofthe light.

In one variant illustrated in FIG. 5, the optical output is rigidlyattached to a container 40 filled with liquid intended to constitute thetransparent medium. The treatment system 15 comprises a handpiece 42 onwhich is mounted a reservoir and which supports the optical output.

The hairs may pass through a treatment space in which emerges an orificethat is in communication with the reservoir.

The handpiece may be moved along the hairs.

The irradiation may take place automatically, as a function of themovement, and/or may be controlled by the operator.

Needless to say, the invention is not limited to the examples that havejust been described.

The expression “comprising one” should be understood as being synonymouswith “comprising at least one”, unless otherwise mentioned.

1. A method for treatment of hair of the scalp, comprising: exposing atleast a portion of at least one hair of the scalp to at least one lightpulse through a transparent medium that is fluid or that has solidified,wherein a refractive index of the transparent medium is greater than orequal to 1.3, the transparent medium is in contact with the scalp hairand extending between the scalp hair and a surface for the entry oflight into the medium.
 2. The method according to claim 1, wherein ashape of the light entry surface is defined by a transparent wall of anirradiation device in contact with the transparent medium.
 3. The methodaccording to claim 1, wherein a shape of the light entry surface isdefined by levelling or flattening the medium prior to the exposure tothe light pulse.
 4. The method according to claim 1, wherein an entiresection of at least one treated hair is included in the transparentmedium.
 5. The method according to claim 1, wherein at least two layersof superposed hairs are included in the transparent medium and aresimultaneously exposed to the light pulse(s).
 6. The method according toclaim 1, wherein the treated scalp hair is confined in a guide systemdefining a treatment space comprising the scalp hairs and thetransparent medium.
 7. The method according to claim 7, wherein thescalp hairs are packed into the treatment space.
 8. The method accordingto claim 1, wherein a peak power of the light pulse is greater than orequal to 10⁵ W.
 9. The method according to claim 1, wherein thetransparent medium comprises at least one organic compound in a masscontent of greater than or equal to 25%.
 10. The method according toclaim 1, wherein the transparent medium is dispensed on the scalp hairsfrom at least one orifice for delivering said transparent medium,occupying a variable position relative to the scalp hairs, between twolight pulses.
 11. The method according to claim 1, wherein a refractiveindex of the medium is greater than or equal to 1.4.
 12. The methodaccording to claim 1, wherein the scalp hairs are bleached, modified inshape or bleached and modified in shape.
 13. The method according toclaim 1, wherein the duration of the pulses is greater than 5×10⁻¹² s.14. A scalp hair treatment system, comprising: a source of pulsed light,a source of a fluid or solidifiable transparent medium, having arefractive index of greater than or equal to 1.3, a system for guidingthe scalp hairs to be treated, configured to receive the scalp hairs tobe treated, wherein the treatment system is configured to bring thetransparent medium into contact with the scalp hairs to be treated. 15.The system according to claim 14, wherein the treatment space exposed tothe light pulses surrounds the treated scalp hair(s) on all sides, in atleast one section taken transversely relative to the treated scalphair(s).
 16. The method according to claim 1, wherein the surface forthe entry of the light into the medium is of a predefined shape.
 17. Thesystem according to claim 14, wherein the system is configured to definea surface of predetermined shape for entry of light into the medium.